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Very fine crystalline or glassy rock of volcanic origin, composed chiefly of sodic plagioclase and free silica with subordinate dark-colored minerals.



a magmatic rock that is the effusive equivalent of granodiorite and quartz-diorite. Dacite consists of a finegrained or vitreous basic mass and phenocrysts of plagioclase and quartz, more rarely, of hornblende, biotite, and pyroxene, and sometimes, sanidine. Where albitization processes are widely developed, dacite turns into quartz al-bitophyre. Dacites were ejected by volcanoes in the Paleozoic (in the Urals, for example), Mesozoic, and Cenozoic (in the Caucasus, for example). They are also found among modern lavas on Kamchatka.

References in periodicals archive ?
The population distributions of the Zanbil adakitic dacites were modeled by mixing together two populations of crystals with linear CSDs, termed fine grains and phenocrysts, for both amphibole and plagioclase.
Furthermore, residence times for amphibole nuclei and phenocrysts in Zanbil adakitic dacites are twice as long compared to those of amphiboles in the Mutro dyke (Nkono et al.
We have compared the CSD pattern of the plagioclase of Zanbil dacites with other well studied extrusive and intrusive igneous rocks plagioclase CSDs (Fig.
Quantitative textural analysis of a series of samples from the Zanbil adakitic dacites indicates that their textures reflect two separate events during magma evolution and that the adakitic dacites formed by refilling and partial emptying of a magma chamber.
We compared the above CSDs with the Bezow dacites patterns to determine if the trends are similar.
2, apfu) values similar to tschermakite from dacites without disequilibrium features.
It is important to note that the most silicic FDE lavas overlap the F dacites without disequilibrium texture.
F dacites exhibit higher abundances of trace elements compared to most ME, with the exception of compatible elements, Sr, and Y However, SC37a enclave (SCC sector) represents a special case, due to a marked enrichment in REE, Ba, Sr, Zr and Y compared to the other enclaves.
Nixon and Pearce (1987) reported repeated major sharp reversals in plagioclase crystals from Iztaccihuatl dacites due to magma mixing caused by injection of fresh basic magma.
Homblede in top right contains ma tite inclusions, (H) photomicrograph of dacite (KS-9) exhibiting
The dacite is represented by only one variety: hornblende dacite.
In this diagram, 22 samples plot in andesite fields, whereas five from Koh-e-Sultan area and two from Dam Koh area plot in dacite field or just on boundary between andesite and dacite fields.